Evapotranspiration(Evaporation and Transpiration)Although some definitions of evapotranspiration include evaporation from surface-water bodies, such as lakes and even the ocean, according to the US Geological Survey, evapotranspiration is defined as "the water lost to the atmosphere from the ground surface and the transpiration of groundwater by plants through their leaves."It's a mouthful no matter how you say it.
Transpiration is the process in which moisture is carried through plants from roots to small pores on the underside of leaves, where it changes to vapor and is released to the atmosphere. Transpiration is basically evaporation of water from plant leaves. It is estimated that about 10 percent of the moisture found in the atmosphere is released by plants through transpiration. Plant transpiration is an invisible process. Since the water is evaporating from the leaf surfaces, you don't just go out and see the leaves "breathing". During a growing season, a leaf will transpire many times more water than its own weight. A large oak tree can transpire 40,000 gallons (151,000 liters) per year.
The amount of water that plants transpire varies greatly geographically and over time. There are a number of factors that determine transpiration rates: Temperature - Transpiration rates go up as the temperature goes up, especially during the growing season, when the air is warmer due to stronger sunlight and warmer air masses. Relative humidity - As the relative humidity of the air surrounding the plant rises the transpiration rate falls. It is easier for water to evaporate into dryer air than into more saturated air. Wind and air movement - Increased movement of the air around a plant will result in a higher transpiration rate. Soil-moisture availability - When moisture is lacking, plants can begin to senesce (premature aging, which can result in leaf loss) and transpire less water. Type of plant - Plants transpire water at different rates. Some plants which grow in arid regions, such as cacti and succulents, conserve precious water by transpiring less water than other plants. 
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